1. Field of the Disclosure
The present disclosure relates to a technology of estimating rotor time constant of induction motor, and more particularly to an apparatus for estimating rotor time constant of induction motor.
2. Discussion of the Related Art
The information disclosed in this Discussion of the Related Art section is only for enhancement of understanding of the general background of the present disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
In general, vehicles using a motor for a power source such as hybrid electric vehicles (HEVs) and electric vehicle (EVs) require a high level of precise torque control. Recently, an induction motor gains attention as a driving motor for HEVs and EVs as price of permanent magnet-type motor increases due to price increase of rare earth metals.
A technique of executing vector control on an alternating-current electric motor by using an inverter has been broadly used in an industrial field.
Direct vector control or indirect vector control is executed on induction motor, and an indirect vector control is generally performed that has less influence on parameter change of motor.
However, in an induction motor that performs indirect vector control, changes in rotor time constant caused by changes in external factors (particularly, temperature) have an influence on torque generation, and if changes in torque generation increase, problems occur where acceleration performance, riding quality and driving quality change due to external factors. In connection therewith, technology is disclosed in which rotor time constant is estimated in real time to minimize changes in torque generation.
FIG. 1 is a configurative view illustrating an apparatus for estimating rotor time constant of induction motor according to prior art.
In the system like above, a d-axis voltage obtained from rotor parameter may be vdse=Rsidse*−ωeσLsiqse*, and an output of a current controller (110) may be vdse*.
Although these two values must be identical in ideal cases, a difference is generated between calculated slip speed and actual slip speed to make the output (vdse*) of a current controller (110) different from the calculated d-axis output ({circumflex over (v)}dse), if the rotor time constant (τr) is changed by factors such as temperature and the like.
A derivative (Δτr) of rotor time constant is obtained using the difference, and rotor time constant ({circumflex over (τ)}r) used for control is corrected by reflecting to an initial value (τr0) of the rotor time constant.
As described above, the conventional apparatus for estimating rotor time constant of induction motor estimates the rotor time constant, and minimizes the derivative of torque generated thereby.
However, in a case the d-axis voltage is used as above, an actual voltage change resultant from change in rotor time constant (τr) is small, which is due to size of a stator transient inductance (σLs) being small. Furthermore, as a q-axis current (iqse*) is changed by torque command, size of d-axis voltage (vdse) in light load is small to make it insufficient to compensate the changes in rotor time constant (τr).
As noted from the foregoing, the system thus described is problematic in that the system can be applied only if a load reaches a predetermined level, such that a method is being attempted where the d-axis voltage (vdse) is multiplied by speed or d-axis current (idse*).
However, despite the abovementioned attempt, the conventional system still has a problem in that changes in size of d-axis voltage (vdse) during high speed operation are not large enough to detect the changes of the rotor time constant, such that it is not easy to apply the method to EV/HEV driving motor largely using the high speed operation.